Interaction of CO with clean and oxygen covered PdCu(110) single crystal alloy

Abstract

Compositional changes that may occur upon CO chemisorption on PdCu (110) single crystal alloy have been studied by means of work function change measurements using the Kelvin probe technique. Furthermore, various surfaces of this alloy with different surface compositions were investigated with respect to their reactivity in the CO oxidation applying the same technique. It was found that CO chemisorption, in the case of Cu-rich surfaces, induces the segregation of Pd to the surface. High CO pressures (10-4–10-3 mbar) also cause the surface segregation of still unidentified contamination characterized by an AES signal at 180eV. In the CO oxidation experiments the PdCu alloy showed lower reactivities compared to pure Pd, even though the outermost layer was entirely composed of Pd atoms. The reactivity was found to decrease further with increasing Cu concentrations. The lower reactivity of the PdCu alloy was attributed to the charge transfer from Pd to Cu observed in this system resulting in decreasing the adsorption enthalpy (and probably the sticking coefficient) of CO on “modified” Pd of the alloy surface.